1. Technical Field
The present invention relates to a zoom lens, and a device having the zoom lens as an photographing optical system such as a camera and a portable information terminal device.
2. Description of the Related Art
Market of cameras used for security and the like is widened, and demands thereof are also increased in various fields. Especially, with the demands for high image quality and high magnification changeability, in the zoom lens used as a photographing lens, the reconciliation of high performance with high magnification changeability has been desired.
Herein, in terms of high performance, a configuration having a resolving power corresponding to imaging elements of at least 1 mega to 5 mega pixels over the entire zoom range is desirable. It is also considered that a magnification changing ratio of about X20 is needed as the high magnification changeability.
In addition, it is preferable that aberrations be sufficiently corrected even in a near infrared wavelength range so that photographing is available even in a dark state. Further, widening of an angle of view is preferred, and preferably, a half angle of view at a short focal end of a zoom lens is about 30 degrees or more. In addition, a large diameter of a lens is preferred, and preferably, an F number at a short focal end (sometimes, referred to as “wide angle”) is 2.0 or less.
As a type capable of securing a magnification changing ratio of about X20 and suitable for a large diameter of a lens, there has been developed a zoom lens including a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power.
However, none of the zoom lenses satisfies conditions of an F number of 2.0 or less at a short focal end, a magnification changing ratio of about X20, and an F number of 2.0 or more at a long focal end (telephoto end), while achieving a small size and correction of aberration in a near infrared range.